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We have two extant commentaries on Aristotle’s De Anima in late antiquity, containing extensive passages on the theory of sense-perception. One is written in Alexandria and has been attributed to John Philoponus, though the attribution of the part discussing the third book is contested.[1] The other was composed in the circle of Neoplatonists at Athens, and has been traditionally ascribed to Simplicius. Again, the attribution is called into doubt.[2] But even if the authorship of Simplicius is questionable, the fact remains that the work was written by an Athenian Neoplatonist. This allows for a comparison between the methods and devices used in Athens and Alexandria to examine sense-perception.[3] The comparison may indicate significant differences between the approaches of the two schools.

The Athenian commentary is considerably shorter than Philoponus’ work and much more imbued with the Neoplatonic jargon of this age. This may give rise to the assumption that the author’s primary aim was to explain Aristotle’s doctrines in the light of the doctrines of the Platonic tradition, using terms that were not used by Aristotle at all. That might have led to a significant transformation of Aristotle’s doctrines as well. By contrast, Philoponus, and his teacher Ammonius in Alexandria, aimed at clarifying the problems in the De Anima by remaining as close as possible by the Aristotelian terminology.[4] Hence it is understandable that the use of typical Platonic terminology in this commentary is not something which could determine the scope of the whole work.

On discussing the methodical principles followed by John Philoponus we have to note that he seems to be relying more on empirical material.[5] He used this kind of evidence, however, not necessarily with the purpose of proving his case, rather for supporting or illustrating it. As a preliminary to our investigation, we can also see that reliance on empirical material is accompanied with a familiarity with Aristotle’s zoological works as well. Throughout the commentary on De Anima II we find references to these works.[6] The reason why Philoponus recurred to the zoological treatises was partly to back up the thesis he favored. He found arguments there which served his purposes well. A few samples will suffice to illustrate the point. In claiming that fishes can neither breathe in nor breathe out, and therefore they are not capable of speaking either, he believes De Partibus Animalium on his side because it says in 669a3-6 that fishes do not need cooling from air (384.25-26). One of the primary functions of breathing is to cool the internal vital heat.[7] Fishes, however, have water around which supplies this need. But the capacity of breathing is considered vital to producing voices. Furthermore, voice is a kind of sound, and sound is a change in the air. Thus each animal that produces voice, makes it by the aid of the air. Unlike the vast majority of fishes, however certain species produce voice, which calls for explanation. Philoponus believes to get support from De Spiritu, a work belonging to the Aristotelian Corpus but not by Aristotle, where the author states that fishes make sound not through a voice producing organ, but by some movement of the gills (378.8-10). On closing their gills they emit water which gets disturbed in the process of emission and catches up some air. This is what makes a sound. More importantly, in arguing tacitly against Plato of the Timaeus that nothing goes out from the eyes to grasp the visible object he alludes to De Generatione Animalium 780b21 where Aristotle mentions that in a clear sky if one climbs into a deep well one will see the stars, although at the top of the well one will not see them at all (349.5-9). For Philoponus, the difference rules out that we see by emitting rays or fire particles that encounter the particles coming from the visible object. Supposedly, emission of such particles takes place in both cases, which implies that we ought to see the stars at the top of the well too.

Sometimes, Philoponus referred to Aristotelian texts simply for illustrating the point he is about to make. In such cases, the reference does not have any demonstrational force on its own ; it supports or elucidates the argument put forward by other means. For instance, on discussing the capability of the particular senses to apprehend things that are far, and comparing hearing and sight in this respect, he draws attention to Meteorologica II 8, 369b7-9 where we read that we hear the thunder later and see the lightning first because we can see quicker than we can hear. Sight is quicker and apprehends things that are farther away.[8]

If we turn to more substantial matters and examine the method followed in sorting out the problems concerning sense-perception we can see that quite independently from the material he could find in Aristotle’s zoological works, Philoponus also relied on other sources for support. At this point, however, we have to make a distinction between empirical and medical theories. We shall see that he also draws on medical theories that one may not label empirical by ancient standards. Although the difference does not seem crucial when we compare Philoponus’ procedure to the method followed by Pseudo-Simplicius, we still have to see clearly that in this case reliance on medical theories does not involve empirical tendencies by all means.

To take one example, the description of visual process relies on empirical findings.[9] Many facets of this theory have already been examined carefully, and I can do nothing but emphasize again the influence of medical theories on the commentary.[10] As a supplement to such investigations, I can show how medical material concerning vision serves to underline a general point about sense-perception. The text I draw attention to is printed in the apparatus, not in the body text.[11] It starts with a definition of sense-perception, stating that it is nothing but discrimination (κρίσις) of the affection (πάθος) which is produced in the sense-organ by the object of sense.[12] When the objects of sense dispose the sense-organ in a certain way, the power in the sense-organ apprehends the affection brought about there, and it does it by using its own substrate, the sense-organ. Since nothing is affected by itself, only by what is different and unlike, it is reasonable that we do not perceive the sense-organs in their natural state. It is only when they are affected by some humour contrary to their nature that the sense apprehends the affection brought about there. At this point Philoponus raises the following question : if the affection is produced within, and not by an external sense-object, why do we not see the affection in the sense-organ when our eyes are shut ? One answer refers to the lack of medium for an explanation.[13] One might say that it is not clear why the inner source of stimulating the sense organ needs an external medium. The other answer draws on the Galenic notion of optic pneuma. Due to the influence contrary to its nature the optic pneuma is supposed to go out to the air that is lit up. The pneuma has the perceiving power within and by using the air as an instrument or medium it perceives the affection that has come about in its proper substrate, the eye. Because the optic pneuma has gone outside the perceptive power grasps the affection from without. This is why we do not perceive the affection in the sense-organ when the eyes are shut. In that case the optic pneuma is not capable of leaving the eye. As it turns out later, Philoponus rejects the theory, but he accepts that the method of the approach is legitimate.[14]

We can see that the general thesis on sense-perception gives rise to a problem. Two answers are offered. One is a rehearsal of the Aristotelian doctrine of the medium, with some reference to medical material as well. The other is completely un-Aristotelian, recalling Galenic notions that are not empirical in the sense that Galen himself does not seem to rely on observations regarding the thesis.[15] He also draws on medical theories when mentioning that it is by nature that water lacks flavour.[16]

It may be more interesting, however, that the author’s medical knowledge extends not only to the account of the functioning of the particular senses. He is also familiar with an explanation of another type of perception in physiological terms. He raises the question whether the fact that we are aware of ourselves (συναίσθησις) when we are in a too hot or in too cold a state, is due to our perception of the bad mixture of the elements in us. As an answer he refers to the assumptions of the doctors. The relevant text runs as follows :

Λέγουσι πρὸς τοῦτο κάλλιστα καὶ οἱ ἰατροί, ὅτι πυρεττόντων ἢ ψυχομένων ἐν ταῖς νόσοις ἑαυτῶν αἰσθανόμεθα, οὐκ αὐτῶν τῶν αἰσθητικῶν νεύρων ἢ τῶν σαρκῶν τεθερμασμένων, ἀλλὰ τῶν ὑγρῶν αἵματος τε καὶ πνεύματος. ἐπεὶ οὖν ἡ αἰσθητικὴ δύναμις πρώτως ἐν σαρξίν ἐστι καὶ νεύροις, εἰκότως τῶν ὑγρῶν δυσκράτως ἐχόντων, πνεύματος λέγω καὶ αἵματος, παρακειμένων τε τοῖς αἰσθητικοῖς μορίοις τῇ θίξει ἀντιλαμβανόμεθα αὐτῶν, ὥσπερ καὶ τοῦ ἀέρος τεθερμασμένου ἢ κατεψυγμένου τῇ θίξει διὰ τὴν παράθεσιν ἀντιλαμβανόμεθα. κἂν αὐτῶν δὲ τῶν στερεῶν ἅψηται ὁ πυρετός, ἐπειδὴ μὴ ὁμαλῶς θερμαίνεται ἀλλʹ ἀνωμάλως, πάντως εἰσί τινα μὲν μόρια κατὰ φύσιν ἔχοντα, τινὰ δὲ παρὰ φύσιν. συμβαίνει οὖν τὰ ἔτι κατὰ φύσιν ἔχοντα ἀντιλαμβάνεσθαι τῶν παρὰ φύσιν διακειμένων· ἀδύνατον γὰρ ὁμαλὴν γενέσθαι τὴν δυσκρασίαν· τότε γὰρ ἐπὶ φθορὰν λοιπὸν τὸ ζῷον ὁδεύει. αὕτη οὖν αἰτία τῆς συναισθήσεως.[17]

The doctors too say well in reply to this that when we are suffering fever or chill in disease we perceive ourselves, not [through perceiving] the perceptual nerves themselves or the warmed flesh, but the liquids made up of blood and pneuma. Since, then, the power to perceive is primarily in flesh and nerves, it is reasonable that when the liquids, I mean those consisting of pneuma and blood, are in a badly mixed state, since they lie near in the perceiving parts, we should apprehend them by contact, just as too we apprehend warmed and chilled air by contact because of its being near. Even if the fever touches the solid [parts] themselves, since the warming is not even but uneven, there must be some parts that are in their natural state and some in a state that is contrary to nature. It happens, then, that the parts which are still in their natural state apprehend those that are in a state contrary to nature. For it is impossible that the bad mixture should occur evenly, for then the rest of the animal would be on the way to destruction. That is, then, the cause of self-awareness.[18]

Now, as it turns out in the subsequent passage, Philoponus has nothing to object to this interpretation, and thus he is ready to account for perception of the internal states in a way that differs from what Aristotle says about the various forms of sense-perception in the De Anima.[19] The new thesis is elucidated with reference to the change in the pneuma and the blood. There are two questions to be settled. The first is terminological. What is the meaning of συναίσθησις in the passage ? Does it mean consciousness in general, or perceptual awareness, or joint-perception ? To start with the last option, I do not think that we are dealing with joint-perception here. Philoponus does not mention that perception of bodily states must accompany perception of external objects. Instead, he speaks about a direct perception of a certain disordered state in the body without alluding to any other component in the process. It is equally unlikely that he is referring to perceptual awareness. Talk about the awareness that we perceive is entirely missing from the passage. He seems to dismiss it altogether when saying that we perceive ourselves not by perceiving the nerves, which are the seat of the power to perceive. The theory he is alluding to might say that at the level of physiology perceptual awareness takes places when we somehow apprehend the activities of the nerves. It is also important to bear in mind that the term does not play any role in the discussion of perceptual awareness in the commentary on De Anima III 2.[20] Philoponus does not talk about consciousness in general either. The context is very specific since it is about the way we perceive ourselves when we are ill.

These options being excluded it seems that Philoponus talks about a kind of awareness of bodily states, although he introduces the whole passage with the statement that we perceive ourselves. He is not going to convince us that we perceive ourselves by perceiving that our perceptual power is at work. Rather, the thesis he puts forward concerns the perception of our inner states that contribute to what we are. After all, he is discussing how we perceive ourselves. We apprehend these states when our natural condition is deteriorating. It is important that Philoponus says not that we apprehend our inner states, but that we apprehend ourselves.[21] The formulation may be somewhat vague, but so much is clear that the author does not make a radical shift between body and soul, assuming that the latter is what makes out our self. On this thesis, changes in bodily state also make an impact on the way we can apprehend ourselves by way of perceiving the badly mixed states of pneuma and blood. In the same vein, perception of such ingredients may also amount to self-perception. In sum, the “ourselves” seems to extend to certain bodily processes as well.

But the crucial question concerns the description of this kind of self-awareness. It turns out that we perceive our internal states by the aid of touch. As a kind of inner sense, touch enables us to discern the disturbed state of the liquid consisting of blood and pneuma, which leads to a certain kind of awareness. The sense of touch resides in the flesh and the nerves and they contact the liquid mixed from pneuma and blood. The process of perception is based on the difference between parts in natural, and parts in unnatural state. The lack of balance between those parts initiates an alteration ; the part in its natural state apprehends those which are in a state contrary to nature. Thus this kind of self-awareness is due to an inner disharmony among the parts of the moisture in the body.

He tackles another problem in 403.18-36, which is related to the problem of perceptual awareness but cannot be equated with that. He comments on Aristotle’s use of the term “cannot be seen” (ἀόρατος). The term may refer to what cannot be seen by nature, but it may also to what is by nature such as to be seen, although it is not seen actually. The reason why it is not seen is a certain lack. Philoponus’ example is a transparent object which cannot be seen when light does not fall upon it. He claims that in this case “sight apprehends that what cannot be seen cannot be seen”.[22] It is supported by the thesis that non-rational animals also discriminate incidentally by sight that it is dark for they are affected by visible objects. This is why they are remaining in their lairs. One might think that it is a typical line of thought starting from an empirical observation (non-rational animals remain in their lairs in the dark) and leading to a thesis that explains the initial observation. The conclusion, in turn, serves to illustrate a general point on sense-perception, that it is the sight that grasps that what cannot be seen cannot be seen. As all sorts of analogical reasoning, this one also has its own limitations. It does not respond to the objection that the senses may be inactive when they are not affected. Sight cannot function in the dark for we do not see colours in the dark, black being not a colour. The failure may be responsible for a new proposal : it is perhaps φαντασία and not sight that apprehends that which is not seen by virtue of a lack of any proper object. Alternatively, one might suggest that the sense can function independently from the impact coming from the sense object.[23]

It also seems that Philoponus has a general view in the commentary that justifies the frequent recurrence to empirical material. One may ask for the reason for such a procedure. A possible explanation is found in 307.33-308.2 where he puts forward the following thesis :

[…] because the existence of universals too is in particular, but when they are taken as universals and common they come to be in the soul. For their existing as common consists in this, that their commonness is thought of, and thoughts are in the soul. “That is why thinking rests with the person himself”, not with the soul, that is, with the person who has the soul.[24]

This is clearly an Aristotelian thesis, but it is interesting to see that Philoponus does not distance himself from the formulation. It is all the more important because he in this way seems to dissent from the view endorsed by his fellow Platonists at Athens that certain universals belong to the core of the soul and are not empirically acquired. If all the universals are in the particulars and the soul only acquires them as common to many particulars, then the only way to get hold of universal notions (νοήματα) is to grasp them via sense-perception. Such a methodical principle justifies recurrence to medical material, and also explains Philoponus’ effort to seek empirical evidence for some of the theses proposed in the commentary.[25]

To see the difference in detail, we can now turn to Pseudo-Simplicius’ commentary. We find a completely different approach there. The author has nothing to say about the physiological processes that might accompany the activity of sense-perception.

First we have to draw attention to the formal differences. On discussing sense perception in general, the Athenian commentator seems to ignore medical material whatsoever. More strikingly, he hardly makes any reference to the biological treatises of Aristotle.[26] His examination of the matter is centred around the general questions of alteration and the role of judgment in sense-perception. That led over to the question about the extent to which reason is involved in sense-perception. He prefers the examination of concepts and strict exegesis of Aristotle’s text with frequent comparisons with Plato’s doctrines. There is no attempt to reflect on questions posed by empirical observations and medical theories.

The method he follows in examining the functioning of the particular senses is appropriate to these principles. We might take the paradigmatic case of sight first. If we examine how this commentator discusses the question of seeing in the dark, we see that methodical differences result in different views. As we have seen, Philoponus cannot rule out that the sense of sight itself is unable to perform this task. It is perhaps φαντασία that is responsible for the lack of impact on the senses. By contrast, Pseudo-Simplicius insists that sight is capable of perceiving in the dark. To put it more precisely, he says that sight on its own can judge that it is dark.[27] The argument is peculiar and has an important result. Darkness is deprived of colours, which are the primary objects of sight. Since sight does not apprehend any colour in the dark, it must turn to other resources for apprehending that it is dark. It is capable of judging it, not by seeing anything, by not seeing. It becomes aware of the dark by the attempt to see. The thesis can be generalized : all kinds of primary sense-perception can work in this way. The wording makes it also clear that perceptual judgment pertains to a state of affair, not to a quality, since there is no quality around to be perceived.[28] Hence it is obvious that Pseudo-Simplicius’ explanation is radically different from the one proposed by Philoponus. His argument is straightforwardly deductive. He takes over Iamblichus’ doctrine that the soul is fully permeated by reason. Hence sense-perception is also rational in an appropriate way.[29] As one of the hallmarks of rationality is reflection, sense-perception must also be capable of reverting to itself. Reversion amounts to the apprehension of the activity of its own, which in the case of sense-perception results in perceptual awareness.

The commentator connects perceptual awareness with the capacity of apprehending that the special sense-objects are not around. The passage immediately follows the one discussed above. It runs as follows :

οὐ τῷ ὁρᾶν τι τὸ σκότος ἡ ὄψις κρίνουσα, ἀλλ᾿ αὐτῷ τῷ μὴ ὁρᾶν ἐν τῷ πειρᾶσθαι ὁρᾶν συναισθανομένη αὐτοῦ, διὰ τοῦτο μόλις ὁρώμενον. καὶ τοῦτο ἴδιον τοῦ ἄνευ φωτὸς διαφανοῦς τὸ ὁπωσοῦν ὁρᾶσθαι, εἰ καὶ μὴ κατ᾿ ἐπιβολήν· ὡς τά γε χρώματα ἀόρατα μὲν καὶ αὐτὰ χωρὶς φωτός, ἀλλ᾿ οὐδὲ πειρωμένοις ὁρᾶν παρέχεται ὁποιανοῦν ἑαυτῶν συναίσθησιν.[30]

Since sight does not judge that it is dark by seeing anything, but by just not seeing, becoming aware of the dark in the attempt to see. So it is “scarcely something seen”. This is proper to the transparent without light, to be seen in some way, even if not through intuition. Just as colours are themselves invisible without light, but yet when one is trying to see them, they do provide a kind of awareness of themselves.[31]

The fact that the issues are intimately connected is another sign of difference between the two commentators. Furthermore, the crucial terms are used unambiguously by Pseudo-Simplicius to delineate the connection. By συναίσθησις he means perceptual awareness, that the sense is capable of apprehending its own activity. What the sense of sight apprehends in the dark primarily is the activity of its own, which is its attempt to see. Similarly, the use of κατ᾿ ἐπιβολήν underlines the possibility that the intellect may be involved in this process. As elsewhere in the commentary, the term may mean an act of the intellect which makes use of sense-perception and does not pertain to intelligible entities.[32] This possibility is denied with the claim that we somehow apprehend colours, the proper object of seeing, vaguely and indirectly. They provide a certain awareness of themselves. The thesis seems to be the upshot of a deductive reasoning. The commentator never refers to observation or experience to support that claim.

Another result of the inquiry is the thesis according to which the sense can work without being acted on by the sense object. If the sense is capable of attempting to perceive in the absence of the any proper sense object then it must be capable of functioning independently of the influence of the sense object. This seems to signal an important dissent from the Aristotelian theory where the sense is activated by the form of the object of sense. On the other hand, it reminds us of Plato’s theory in the Timaeus, that visual perception takes place by the aid of the rays emitted by the eye, with the implication that emission visual rays may go on and on even if sense perception does not come about.

He returns to the problem in the discussion of taste.[33] He examines in general terms what happens to the sense if the impact coming from the sensible object is not moderate. Even if a sense does not perceive its proper object when it tries to do that, by the fact of not perceiving, it is also aware of the lack of its proper object. This object cannot be perceived because of deficiency since the perceptible form is not present in the substrate. Following this logic, unlike Philoponus, Pseudo-Simplicius also asserts that the sense can recognize the excessive sensible object, an object exerting excessive, and thus harmful, influence on the sense.[34] The sense cannot adjust itself to the sense object as it is either deficient or excessive. But that does not mean that it cannot recognize it. The overall claim is that imperceptibility is said in two ways. Something is imperceptible if it has such a nature as to rule out perceptibility. As an example of a limited range, the commentator mentions voice which is invisible. On the other hand, we call a thing imperceptible if it lacks the perceptible form, although it is of a nature to have it. In the latter case, the sense is capable of recognizing (but not perceiving in the strict sense) what is imperceptible. Thus one can say that the taste is both of the tasty and of the tasteless. Again, the method he follows in this inquiry is strictly confined to conceptual analysis (two senses of the “imperceptible”) and devoid of any reference to medical material. It is by such means that he reaches the conclusion that the senses can work even if no sensible object proper to them is around or cannot be perceived because of the feature of the medium, which is the case when we enter a dark room from a sunny place.

If we want to make a short comparison between the methods used by the two commentators, the first thing to note is the difference in the material they rely on. The Alexandrian commentator draws both on the material collected in Aristotle’s biological works and on the medical ideas to be found in later authors. By contrast, Pseudo-Simplicius never claimed to get support from such sources. On explaining the theories in the De Anima he uses deductive arguments, the premises of which are mostly in Aristotle’s psychological works. Furthermore, he constantly makes use of theories, worked out for the most part by Iamblichus, which do not show much affinity to medical or biological theories. Using different theories as source of inspiration was accompanied with to different methods of inquiry. It has been shown that Philoponus relied on medical material extensively, and sometimes used it to illustrate, sometimes to underpin theses concerning the features of the soul.[35] Discussion of sense-perception is characterized by frequent references to medical theories and observation. That does not mean, however, that he accepts them all uncritically. Rather, they offer the background against which Philoponus has to formulate his own ideas. Speaking in Aristotelian way, they form part of the ἔνδοξα. Pseudo-Simplicius does not seem to have made any effort to employ such devices in the commentary on the De Anima.

We can see, then, that the two approaches are very different. Philoponus reflects on problems raised by medical authors and uses empirical material extensively, either to illustrate the point he is about to make, either to employ it as an independent argument. By contrast, his Athenian contemporary Pseudo-Simplicius passes up every chance for including medical findings in the discussion of Aristotle’s theory. His approach is deductive insofar as he takes a few general doctrines as guidelines by the aid of which to explain the text. As a conclusion, it seems that the examination of this peculiar subject might give the impression that there is still something relevant in Karl Praechter’s characterization of the Alexandrian versus Athenian Neoplatonism in the 5th and 6th century. It does not mean that we are entitled to draw such a clear line between the two schools again. But there seems to be a difference in nuances that should be spelled out. The distinction itself cannot be dismissed altogether.[36]